This invention relates to multi-keying circuitry for keying several fill video signals such as titles into a background television video signal in response to keying signals.
In particular, the present invention provides an economical and operationally attractive means of simultaneously keying such titles or other sources into a television picture.
It was the realization that such fill video signals (or keys) usually each occupy a defined area of the screen that made it possible to design a multikeyer in which the innovative idea is the time-sharing of circuits. The circuit functions are adapted in each screen area by parameters which define the requirements of each key.
This system takes advantage of the fact that in most keying situations, when it is desired to have a number of simultaneous titles, they are generally not placed over one another in layers, rather they each occupy various defined areas of the TV screen. It is usual to start with a basic picture, upon which a number of keyed images such as titles, messages or other keying sources are individually placed in some desired sequence. Such keyed images may later be removed either separately or in groups.
For example, much of TV production is directed to the making of commercials. Such commercials are composed by editing pre-recorded material. During the editing process, titles and other image material are added using a video keying process Because the location where these images are to be placed on the screen is known in advance, the area of the screen where a particular title, etc. is to be placed may be defined, usually by describing a suitably placed rectangle. Such rectangles are usually non-overlapping and shall be referred to as masks. A mask defines the limits of an area in which a keyed image having a particular set of parameters may exist. This invention however is not restricted to the use of rectangular masks, this simply being a function of the mask generator design. The rules for satisfactorily dealing with overlapping masks may also be defined.
An important object of this invention is therefore the provision of a multi-keyer which time shares circuitry associated with or ancillary to the video keying process. The resultant multiple usage of complex circuits provides a very economical alternative to the keying approach of prior art, which required a separate set of keying and ancillary circuits for each keyed area on a television picture. The time-sharing system has been designed to respond with sufficient rapidity that the keying and ancillary circuits may be sequentially configured with the parameters which may simultaneously exist in separate areas of a television screen.
It is a further object of this invention to provide improved control circuitry for time sharing the keying circuits of a multi-keyer.
As a further object of this invention to employ dual port rams to facilitate the time sharing of the keying circuits of a multi-keyer.
It is a further object of the invention to use, in a time sharing multi-keyer, a digital-to-analog convertor such as a RAM-DAC (which is typically used for video picture signals) as a digital-to-analog convertor for digitized linear (or analog) control parameters associated with the keyed images.
It is a further object of this invention to provide, in a multi-keyer, improved circuitry for effecting transitions between keyed images either separately or in groups.
It is a further object of the invention to provide, in a multi-keyer, improved circuitry for previewing not only the keyed areas but also the transitions thereto.
These and other objects of the invention will become apparent from a reading of the specification taken with the appended drawings and claims.